1. Field of the Invention
The present invention relates to a volume data encoder in the field of digital image processing, and in particular to a volume data encoder for encoding image data having a three-dimensional pixel arrangement (hereafter referred to as volume data) with high efficiency.
2. Description of the Related Art
It has become possible to acquire a large amount of three-dimensional medical image data in the department of radiology as a result of the renovation in the technique such as the CT and MR. Needs for compression of such images are becoming greater.
In DICOM (Digital Imaging and Communications in Medicine), which is standards for a system intended for storage and management of images in the department of radiology, JPEG (irreversible encoding) and JPEG-LS (reversible encoding), which are two-dimensional-based image encoding systems, are approved as the compression system for such images.
In encoding, and especially in reversible encoding, using the conventional two-dimensional-based image encoding as described above, there is a limit in the encoding efficiency of data. In some cases, therefore, compression brings about neither a remarkable reduction of the server capacity for storing encoded data, nor shortening of the time required for transmission. Three-dimensional wavelets are frequently used for encoding volume data. As a preceding paper concerning the three-dimensional wavelets, for example, Japanese Patent Application Laid-Open Publication No. 2002-204168 can be mentioned.